A 2-week-old male infant born at term is found to have bilateral renal hydronephrosis on postnatal ultrasound performed at day 7 of life. The structure marked **B** in the diagram shows Society for Fetal Urology (SFU) grade 3 hydronephrosis with dilation of the renal pelvis and all calyces without parenchymal thinning. Voiding cystourethrogram (VCUG) reveals bilateral vesicoureteral reflux and a dilated posterior urethra with a characteristic "keyhole" appearance. Which of the following is the most likely underlying diagnosis?
A. Posterior urethral valves (PUV)
B. Vesicoureteral reflux (VUR) alone without obstruction
C. Ureteropelvic junction (UPJ) obstruction
D. Ureterocele with duplex kidney
Explanation
Why Posterior urethral valves (PUV) is right
Posterior urethral valves are the most common cause of BILATERAL hydronephrosis with bladder distension in male newborns. The clinical presentation of a male infant with bilateral high-grade hydronephrosis (SFU grade 3, as marked in structure B), dilated posterior urethra with "keyhole" appearance on VCUG, and secondary vesicoureteral reflux is pathognomonic for PUV. The bilateral nature and male sex are key discriminators. PUV requires emergent endoscopic valve ablation in the neonatal period to prevent progressive renal function loss. [AAP Guidelines on UTI 2024; UTD Consensus 2014]
Why each distractor is wrong
Ureteropelvic junction (UPJ) obstruction: While UPJ obstruction is the most common cause of significant hydronephrosis in children overall, it is typically UNILATERAL (90% of cases) and does not cause the characteristic "keyhole" urethra or secondary VUR seen on VCUG. The bilateral presentation with urethral findings excludes this diagnosis.
Vesicoureteral reflux (VUR) alone without obstruction: VUR can cause hydronephrosis, but the presence of a dilated posterior urethra with "keyhole" appearance is not a feature of primary VUR. The urethral findings indicate an obstructive lesion at the level of the posterior urethra, not reflux alone.
Ureterocele with duplex kidney: Ureteroceles typically present with unilateral or upper-pole moiety hydronephrosis in the setting of a duplex kidney (Weigert-Meyer rule). They do not cause bilateral hydronephrosis or the characteristic posterior urethral findings seen in this case.
High-YieldNEET PG
Bilateral hydronephrosis + "keyhole" urethra + male infant = PUV until proven otherwise; endoscopic valve ablation is the definitive neonatal intervention.
AAP Guidelines on UTI 2024; Society for Fetal Urology Hydronephrosis Grading; UTD Consensus 2014
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